Initiate a new bulk sequence subscription
`action_type` must be one of:
- `subscribe` to create a new sequence subscription for contacts that have never received the given sequence.
- `resume` to resume any paused sequence subscriptions for the given sequence or all sequences if `sequence_id` is not provided.
- `resume_finished` to resume any finished sequence subscriptions for the given sequence or all sequences if `sequence_id` is not provided.
- `pause` to pause any active sequence subscriptions for the given sequence or all sequences if `sequence_id` is not provided.
`sequence_id`, `sender_account_id`, `sender_name`, `sender_email` and `contact_preference` are required if `action_type` is `subscribe`.
`contact_preference` can be set to:
- `lead` to only subscribe the primary/first contact email of the lead.
- `contact` to subscribe the primary email of each contact of the lead.